powerpc: MPC8548: Move CONFIG_MPC8548 to Kconfig option

Replace CONFIG_MPC8548 with ARCH_MPC8548 in Kconfig.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 9bcbda0..530c232 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -10,6 +10,7 @@
 
 config TARGET_SBC8548
 	bool "Support sbc8548"
+	select ARCH_MPC8548
 
 config TARGET_SOCRATES
 	bool "Support socrates"
@@ -63,6 +64,7 @@
 
 config TARGET_MPC8548CDS
 	bool "Support MPC8548CDS"
+	select ARCH_MPC8548
 
 config TARGET_MPC8555CDS
 	bool "Support MPC8555CDS"
@@ -156,6 +158,7 @@
 
 config TARGET_XPEDITE520X
 	bool "Support xpedite520x"
+	select ARCH_MPC8548
 
 config TARGET_XPEDITE537X
 	bool "Support xpedite537x"
@@ -172,6 +175,9 @@
 
 endchoice
 
+config ARCH_MPC8548
+	bool
+
 source "board/freescale/b4860qds/Kconfig"
 source "board/freescale/bsc9131rdb/Kconfig"
 source "board/freescale/bsc9132qds/Kconfig"